Title: Experimental Evidence on Reducing Youth Violence and Improving Life Outcomes in Chicago The broad aim of this proposal is to carry out a large-scale RCT that tries to use intensive mentoring to engage and retain those youth at highest risk for violence involvement in a five- month behavioral-science-informed intervention focused on decision making to decrease violence involvement (trauma-informed cognitive behavioral therapy, or CBT). This study of Choose to Change (C2C) is submitted in response to R01 ?Research Grants for Preventing Violence and Violence Related Injury? (RFA-CE-18-001) under Objective B. This project addresses the mission of the Centers for Disease Control and Prevention by generating evidence on what works to address the public health challenge of youth violence. The specific aims of the project are as follows: 1) Complete the RCT currently underway, to ensure enrollment, random assignment and program delivery are all carried out with maximum fidelity, 2) Generate final impact estimates of the causal effects of C2C on behavioral outcomes (youth violence) using data from the Chicago Police Department and academic outcomes from the Chicago Public Schools, and identify differential responses across youth (treatment heterogeneity), 3) Measure the spillover effects of C2C on peers, 4) Identify and understand the behavioral mechanisms behind the impacts we find, 5) Identify the cost-effectiveness of this approach, 6) Disseminate these findings through publication in a top-tier peer-reviewed scientific outlet, complemented by other outreach activities oriented towards policymakers and practitioners, 7) Document and manualize the C2C therapy curriculum for the purpose of supporting replication. The present proposal requests funding for three years to carry out these aims. The sample size is 1,600 youth randomized over the 2015 to 2018 period, with almost 500 program participants. Eligible youth are referred by school and community partners who have been identified as being at risk for violence involvement. The research will be led by PI, Dr. Jens Ludwig, and supported by a team at the UChicago Crime Lab. The use of intensive mentorship to enroll the highest-risk youth in programming is one innovation. Another is the use of administrative data to measure social networks at low cost, which lets us test how peer networks moderate program impacts and are also affected by the program. A final innovation is to administer behavioral science ?lab experiments? to treatment and control groups in our field RCT to learn more about mechanisms of action. We believe the results of this research will be of great policy and public health value to cities across the US in finding methods to prevent youth violence to improve the safety and life outcomes of their most vulnerable young people.